Optical networks are used in telecommunication and enterprise networks to move data and communications. Optical signals provide high-speed, superior signal quality, and minimal interference from outside electromagnetic energy. Optical networks utilizing Dense Wavelength Division Multiplexed (DWDM) systems offer tunable multi-channel optical links.
Optical networks often include optical modulators, such as a Mach-Zehnder Modulator (MZM). The performance of optical modulators may be affected by numerous factors, such as changes in the environmental temperature. Many of today's optical modulators lack control systems to maximize modulator performance.
For a duo-binary MZM, optical performance is optimized when the MZM operates at a null point. To maintain operation to remain at this null point, a direct current (DC) bias voltage provided to the MZM may be controlled using a so-called DC bias dither method. In this control system, a low frequency signal is added into the DC bias voltage, which is then recovered and processed to control the DC bias voltage by minimizing the error signal, which results in operation at the null point. However, a number of drawbacks exist in this control method. First, a radio frequency (RF) signal amplitude for an incoming data signal must be well controlled because the error signal changes the phase by 180 degrees depending upon the amplitude of the RF signal. Further, the control method does not work when the RF amplitude is at a certain value. Still further, the control loop incurs significant interference when the RF data pattern coincides with the injected low frequency signal.